Keratoconus is a degenerative disorder of the eye in which structural changes within the cornea cause thinning and loss of curvature. Keratoconus can cause substantial distortion of vision, including double vision (diplopia), streaking and hyper-sensitivity to light. Keratoconus is typically diagnosed during adolescence. Debilitating deterioration in vision can occur.
Refractive surgical procedures, such as Laser-Assisted Keratomileusis (“LASIK”), are often prescribed to correct common vision disorders. In general, the LASIK procedure is performed by making a thin flap of corneal tissue, folding the flap out of the way, altering the shape of the cornea by subtracting tissue using an excimer laser, then replacing the flap.
Despite the many advantages of LASIK, severe side effects can occur. For example, halos, starbursts, loss of low-light sensitivity and dryness are common side effects of the procedure. In other less common side effects, the flap may fail to adhere properly to the eye's surface or may cause microscopic wrinkles in the flap called corneal striae. Studies indicate that flap complications occur in from 0.3 to 5.7 percent of LASIK procedures, according to the April 2006 issue of American Journal of Ophthalmology. These flap complications can lead to an irregularly shaped eye surface and distorted vision.
Irregular astigmatism also may occur from LASIK correction that is not centered properly on the eye or from irregular healing after the procedure.
In another side effect, epithelial ingrowth occurs when cells from the outer layer of the cornea, the epithelium, grow under the flap. In some cases, blurred vision and or chronic discomfort can result.
In yet another side effect, diffuse lamellar keratitis (“DLK”), nicknamed “Sands of the Sahara,” results in which an inflammation under the LASIK flap occurs. But if the inflammation is uncontrolled, as in DLK, it can interfere with healing and cause vision loss.
The prior art has provided different methods to compensate for the side effects of LASIK surgery; however, none is completely satisfactory. For example, corneal implants, called “Intacs,” may be prescribed to hold the cornea in place.
Another remedy for LASIK side effects is gas permeable contact lenses, such as scleral lenses, which are prescribed as a cost effective and safe remedy. However, the prior art methods to design and construct sclera lenses, so far, have been ineffective to produce an adequate “fit” at an economical price, so that the remedy cannot be widely prescribed or used.
For example, U.S. Pat. No. 5,570,142 to Lieberman discloses a contact lens for asymmetric aspheric corneas with a peripheral portion to fit peripheral portion of the cornea as determined by scan of subject eye. The contact lens is not substantially greater in diameter than the cornea. The process for manufacturing the lens uses three-dimensional topographic data from points on the cornea. The data is used to shape at least the peripheral portion of the posterior surface of the lens. However, the process in Lieberman limited to corneal lenses only and not suitable for scleral lenses.
U.S. Pat. No. 5,452,031 to Ducharme discloses a method for manufacturing a contact lens. The contact lens is made through use of a computer implementing an approximation of the cornea. Piecewise polynomials approximating the corneal topology have equal first and second derivatives where they join. A polynomial representing the central optical portion of the lens and the piecewise polynomial adjacent to the central optical portion curve have an equal first derivative where they join. A contact lens is cut corresponding to the lens surface defined by the piecewise polynomials. However, the method in Ducharme requires an approximation of only the cornea thereby leading to an inaccurate representation of the scleral surface and an uncomfortable fit.
The prior art fails to disclose or suggest a system and method for designing scleral lenses that conform to the shape of the eye surface. Therefore, there is a need in the art for a system and method for designing scleral lenses that accurately follows the shape of the eye surface such that the lens does not rotate when worn or move excessively, and can be worn comfortably and safely on the eye.